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Discussion Starter · #1 ·
Hi all,


I just got my bike back from the dealer after about 3 weeks in the shop.


I was changing oil, and saw it was very milky when I drained it. I put the drain plug back in, put some of the oil into a plastic container for the dealer to verify, and called my insurance company to tow it.


Tow truck picked it up, drove about 80 miles to the nearest dealer, and dropped it off. Side note: it pays to pay that $8 roadside assistance charge for your insurance! It would've cost me at least $100 to tow it myself.


Dealer said the balancer shaft frequently chews through the seals that separate the oil and coolant reservoirs on 2017-2018 Duke 390s. They also said two more bikes came in a few days before they got mine in, with the same issue.


So FYI to all of you with 2017+ bikes out there, especially the 2017-2018 MY, you might run into this issue sooner or later. Just keep an eye out on your coolant levels in the overflow reservoir, and if it starts going down more than once, definitely check oil.


Dealer reassured me it should be much better now, which of course it should, duh.


Let me know if anybody has any questions.
 

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Hi there

Thanks for this information. Can you advise how many miles/km were on your bike when this fault occurred?

Thanks.
 

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Discussion Starter · #3 ·
I think it started consuming coolant at about 1000 miles on the odometer. But I only found the issue at 1800 miles.
 

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Handy information to have thank you for keeping everybody updated , don't suppose you could get mileage data from those other two bikes . Anybody else out there experienced the same problem ? If so at which distance can we find out if it was a bad batch of seals or is it common to all ? Lightning don't panic yet the other problem with internet forums is the paranoia that makes you think all the bad things are going to happen to your bike .
 

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I think the problem will be another than the balancing shaft as there is no oil/coolant separation at this shaft?
 

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Discussion Starter · #8 ·
The cause was the balancer shaft chewing through the seal. They fixed it by removing the engine, disassembling it, replacing the balancer shaft, and putting everything back together.
 

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I’m not sure that this issue “plagues” the 2017 onwards 390 Duke
As the O/P is the only one to have found and reported it. But it’s something to be aware of.
 

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Discussion Starter · #11 ·
That’s not exactly a technical explanation and doesn’t explain what the fault was. What caused the balance shaft to damage the seal?
Not sure, I'll find the documentation tomorrow.


I’m not sure that this issue “plagues” the 2017 onwards 390 Duke
As the O/P is the only one to have found and reported it. But it’s something to be aware of.

In the original post, I mentioned two bikes with the same issue came in just before mine. So even if it's not widely discussed on the forum, it's far from being a one-off phenomenon.
 

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Based on the limited information, it sounds like a batch of poorly made balance shafts. Fingers crossed

Interestingly and despite a comment earlier, the balancer shaft parts diagram doesn’t show any seals.
 

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Too slow on the edit. Presumably the special screw seats into the shaft seal ring to drive the water pump (if that is what drives it). Replacing the balancer shaft does suggest a manufacturing issue with a batch of shafts.
 

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Based on this diagram, the thing that drives water pump's impeller is probably machined on the shaft:
https://www.ktmpartspro.com/oemparts/a/ktm/5ad1028eeb0bed9250b449c5/balancer-shaft

And the seals are shown on this diagram:
https://www.ktmpartspro.com/oemparts/a/ktm/5ad107dfeb0bed9250b449d4/water-pump


Part 10 on the first diagram appears to fit into part 12 on the second diagram. Given the balancer shaft is supported by two bearings, it shouldn’t cause issues unless there is a manufacturing error in the part or perhaps an assembly error where the driving screw comes loose.
 

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Part 10 on the first diagram appears to fit into part 12 on the second diagram. Given the balancer shaft is supported by two bearings, it shouldn’t cause issues unless there is a manufacturing error in the part or perhaps an assembly error where the driving screw comes loose.
I think he is absolutely right. Its impossible that the balancer shaft could cause any of this. Obviously the bolt wasn't tightly bolted causing the washer to fail and mix coolant with oil. I have found so many bolts not properly tighten in my own duke. Thankfully the engine head 4 bolts where properly tightened at more than 50 Nm.

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Discussion Starter · #20 ·
Part 10 on the first diagram appears to fit into part 12 on the second diagram. Given the balancer shaft is supported by two bearings, it shouldn’t cause issues unless there is a manufacturing error in the part or perhaps an assembly error where the driving screw comes loose.
I think he is absolutely right. Its impossible that the balancer shaft could cause any of this. Obviously the bolt wasn't tightly bolted causing the washer to fail and mix coolant with oil. I have found so many bolts not properly tighten in my own duke. Thankfully the engine head 4 bolts where properly tightened at more than 50 Nm.

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What you said contradicts what Mirius said.


It is indeed possible that the balancer shaft causes the leak if it chews through the seals, and Mirius obviously allows for that by saying that it's possible that there is a manufacturing error. Which exactly matches what dealer said.
 
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